Static cast molding of contact lenses involves casting a contact lens in a mold cavity formed by two mold sections, an anterior mold section including a molding surface for forming the anterior lens surface and a posterior mold section including a molding surface for forming the posterior lens surface. Representative static cast molding methods are disclosed in U.S. Pat. No. 5,271,875 (Appleton et al.), U.S. Pat. No. 4,197,266 (Clark et al.), U.S. Pat. No. 4,208,364 (Shepherd), U.S. Pat. No. 4,865,779 (Ihn et al.), U.S. Pat. No. 4,955,580 (Seden et al.), and U.S. Pat. No. 5,143,660 (Hamilton et al.).
Following casting of the lens, the mold assembly is disassembled and the lens is removed from the mold assembly.
One approach for recovering the contact lens involves exposing the entire mold assembly, including the two mold sections and the molded lens therebetween, to an aqueous solution (including water alone). Hydrophilic lenses absorb water to form a hydrogel, and when the lens absorbs water, it swells and is released from both the posterior and anterior molding surfaces of the respective molds. Often, the aqueous solution may also facilitate separation of the two mold sections from each other. The lens can then either be separated from the mold sections, either manually or with automated handling equipment. Representative xe2x80x9cwet releasexe2x80x9d methods are discussed in U.S. Pat. No. 5,264,161 (Druskis et al.).
A second approach involves, initially, a xe2x80x9cdecappingxe2x80x9d step, i.e., separating one mold section from the second mold section with the lens being retained in the second mold section. Then, the lens is removed (or released) from the second mold section, either by exposure to an aqueous solution (wet release) whereby the lens absorbs water to facilitate its separation from the molding surface of the mold section, or by simply removing the lens from the second mold section without the use of an aqueous solution (dry release).
Although the decapping and release operations may seem straightforward, various problems have been encountered. This is especially true for cast molding methods where the molding operation results in the two mold sections being held tightly together, or where the lens has a tendency to stick to one or both molding surfaces of the mold sections. For example, when the first mold section is decapped from the second mold section with the lens being retained in the second mold section, the surface of the lens may be damaged as pieces of lens stick to the first mold section. Also, since the lens has not yet been hydrated, it is brittle, and the decapping operation can fracture the lens.
As another example of problems encountered, it is often desirable that the lens is selectively retained in a desired mold section to minimize manual handling or inspection. However, the decapping process can result in the lens not being retained in the desired mold section as intended, thus requiring manual handling or inspection to ensure that the lens is not discarded with the mold section removed in the decapping process. Various approaches for selective retention of the lens in a desired mold section have been proposed. U.S. Pat. No. 5,271,875 (Appleton et al.) discloses using mold sections made of different materials, however, this complicates the injection molding process. It is also known to treat one of the mold surfaces with plasma treatment to facilitate selective retention of the lens, however, this process adds additional steps and cost to the overall molding process.
Consider the case where it is desired to retain the molded lens on the anterior mold. A decapping operation of which applicant is aware involves decapping the posterior mold (i.e., separating the posterior mold from the anterior mold and molded lens) by holding the anterior mold firmly (for example, in a collet), followed by pulling the posterior mold or by pushing the posterior mold from the anterior mold (for example, with collet fingers). Applicant has found that this approach provides some success, however, yield is not entirely satisfactory due to damage to lenses during the decapping step, or lenses not being retained with the anterior mold as intended. Another approach would involve decapping the posterior mold by holding the posterior mold, followed by applying pressure to the anterior mold to separate the anterior mold and the lens from the posterior mold. However, this approach is less successful than the aforementioned approach in that there is a higher rate of lens damage and/or occurrence of the lens not being retained in the anterior mold.
The operations are further complicated by the fact that many static cast molding methods result in a ring of cured excess lens material being obtained in addition to the molded lens. Thus, while it is generally desirable that the lens is selectively retained in one desired mold section, as discussed above, it is often also desirable that the ring of cured excess lens material be selectively retained on the other mold section.
The invention provides a method that includes a decapping operation to separate one mold section from a second mold section and a contact lens. The method provides improved reliability that the lens is retained selectively on the second mold section as intended. Additionally, the potential for damage to the lens during decapping is reduced. Accordingly, yield can be increased while minimizing manual handling or inspection.
According to a first embodiment, the method comprises: disengaging the first mold section from the second mold section and contact lens by applying a force to the first mold section in a manner that moves the first mold section away from the contact lens surface and the second mold section while minimizing stresses at an interface of the second mold section molding surface and a contact lens surface in contact therewith, and separating the first mold section from the second mold section with the contact lens being retained in the second mold section.
According to a second embodiment, the method comprises: applying a force to a peripheral region of the first mold section whereby a peripheral region of the first mold section molding surface is first separated from the contact lens surface followed by a central region of the first mold section molding surface being separated from the contact lens surface; and separating the first mold section from the second mold section with the contact lens being retained in the second mold section.
According to preferred embodiments, the lens is retained selectively on a molding surface of the anterior mold section, and a ring of cured excess lens material is removed with the posterior mold section.
The decapping operation may be followed by a dry release operation to release the lens from the second mold section, whereby the lens is recovered in a dry state for post-release processing.
The decapping operation minimizes manual handling of the lens and mold sections. The invention obviates the need for pre-molding operations to facilitate decapping or selective retention of the lens on a desired mold section, such as pretreatment of the mold surfaces, and the invention obviates post-mold operations to assist in decapping, such as application of heat or chemical treatments to the mold assembly.
Additionally, the invention provides apparatus for carrying out the methods of the invention.